First flush reactor for stormwater treatment for elevated linear transportation projects.

First flush reactor for stormwater treatment for elevated linear transportation projects.

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    Final report; Dec. 2007-May 2009.
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  • Abstract:
    The United States EPA (Environmental Protection Agency) MS4 (Municipal Separate Storm Water Sewer System) Program regulations require municipalities and government agencies including the Louisiana Department of Transportation and Development (LADOTD) to develop and implement stormwater best management practices (BMPs) for linear transportation systems to reduce the discharge of various pollutants, thereby protecting water quality. An efficient and cost-effective stormwater BMP is urgently needed for elevated linear transportation projects to comply with MS4 regulations. This report documents the development of a first flush-based stormwater treatment device, the first flush reactor, for use on elevated linear transportation projects/roadways for complying with MS4 regulations. A series of stormwater samples were collected from the I-10 elevated roadway section over City Park Lake in urban Baton Rouge. Stormwater treatment experiments were conducted using three laboratory columns filled with different combinations of filter medium layers. In terms of contaminant removal efficiency, the optimum filter medium combination was found to be (a) a mixture of Smart Sponge and Hydra CX2 in the top layer, (b) zerolite in the next layer, (c) sand, (d) sawdust, and (e) gravel in the bottom layer. Results of the laboratory experiments indicate that the first flush reactor with the optimized filter medium layers is able to remove over 85% of total suspended solids (TSS), 90% of total phosphorus, 99% of NO2-N and NO3-N, and 70% - 90% of fecal coliform bacteria. Tested heavy metals include Al, As, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Na, Ni, P, Pb, Si, and Zn. In general, removal rates of heavy metals through the recommended filter media are higher than 80%. The removal rates of three toxic heavy metals including cadmium (Cd), copper (Cu), and lead (Pb) are higher than 90%. Hydrocarbon levels in the stormwater samples were too low to be detected. Some unsolved problems in the current design of the first flush reactor include the low removal rate (15%-58%) of TKN (Total Kjeldahl Nitrogen) and the slight release (up to 20%) of toxic metal zinc (Zn) from the reactor. The problems may be resolved by conducting more column tests and possibly replacing the Hydra CX2 with other types of fiber mulch. Experimental results presented in this report may be used for further study of filter medium selection and for optimization of the first flush reactor. Guidelines for design, field construction, operation, and maintenance of the first flush reactor are provided in this report to help environmental engineers and stormwater managers design and operate the first flush reactor properly and achieve the stormwater pollutant removal efficiency required in the MS4 program.
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